To calculate Eq. (REF ), we need to estimate the densities of \(\mathbf {z}_d^\mathcal {D}, \mathbf {z}_t^\mathcal {D}\)  and \((\mathbf {z}_d^\mathcal {D},\mathbf {z}_t^\mathcal {D})\) .
Based on [1]}, we use the mini-batch weighted sampling as follows:
\( \begin{split}H(\mathbf {z}) &= -\mathbb {E}_{q(\mathbf {z})}[\log q(\mathbf {z})] \\&\approx -\log \frac{1}{M}\sum _{i=1}^{M}[\log \frac{1}{MN} \sum _{j=1}^{M} q\left(\mathbf {z}(\mathbf {x}_i)|\mathbf {x}_j\right)],\end{split}\) 
